A polar bear has been spotted out and about in London - but it's nothing to do with global warming, it's just a publicity stunt for Sky Atlantic's new "Arctic-noir" series, Fortitude.The thriller - which stars Stanley Tucci, Michael Gambon, Sofie Grabol and Christopher Eccleston and starts on Thursday - is set in a fictional town which is home to 3,000 polar bears for every 713 residents.19 prop specialists spent two months designing and building the replica bear, whose movements were controlled (from the inside) by two puppeteers from the hit National Theatre play War Horse.The 8ft-long creature was spotted on London's South Bank and even on the tube - check out today's Big Picture for more sightings.